The present invention relates generally to photovoltaic cells and more particularly to solar cell systems for power generation.
The P-N solar cell is inherently a low voltage device taking the form of a wafer of semiconductor material, such as single crystal silicon. The usual silicon solar cell presently in use for terrestrial power arrays is a disc approximately 7.5 centimeters in diameter and 0.2 millimeters in thickness. The front surface of the wafer contains a p-n junction in the proximity of the surface and has a current collecting metallic grid structure contacting the uppermost layer. The back of the solar cell has a metallic film covering its entire surface and acting as the counter or return electrode. The output of the silicon photovoltaic solar cell is about 0.5 volts open circuit with a current depending upon the exposed area and efficiency of the device, but which may amount to slightly over one ampere for the 7.5 cm. circular terrestrial cell mentioned.
To produce useful quantities of electrical power from silicon solar cells, many must be interconnected in arrays directed at the sunlight. Since each cell by itself produces only a small fraction of the desired power, the cells are organized and interconnected in series-parallel networks which feed bus bars going to power conditioning equipment. The power conditioning equipment converts the direct current to alternating current for transfer by the power company grids to users. Some of the equipment used for power conditioning includes inverters or converters of the static or rotary form, transformers and storage batteries. Much of this equipment is expensive, cumbersome, and requires continual maintenance. In the conversion of direct current solar energy, appreciable losses occur in the power conditioning equipment largely due to hysteresis and joule heating effects. Also, solar energy depends upon sunlight which continually fluctuates in its intensity, particularly in northern climes. Thus, it is desirable to design an `interactive` solar power system which shares load responsibility with the local utility company power sources, such as nuclear or fossil fueled power sources.